1. Field of the Invention
The present invention relates to magnetic record and playback apparatus, more specifically, to a rotary magnetic head assembly for use in a video taperecorder.
2. Description of the Prior Art
A rotary magnetic head assembly for video taperecorders includes a rotary cylindrical drum supported by a driving shaft driven by a motor, a stationary cylindrical drum coaxially disposed with the rotary drum to form a gap therebetween and having substantially the same exterior diameter as that of the rotary drum, and a plurality of magnetic video heads mounted on the rotary drum in the gap in a predetermined phase relationship with each other.
A rotary magnetic head assembly is often provided with a rotary transformer for establishing an electrical connection with external electronics required for recording and playing back video signals on magnetic tape. Such a rotary transformer includes a plurality of primary windings disposed on the rotary drum coaxially with the drive shaft thereof and interconnected with the respective video heads, and the corresponding plurality of secondary windings mounted on the stationary drum coaxially with the drive shaft of the rotary drum and associated with the respective primary windings to establish a magnetic coupling therewith. Conventionally, the primary windings are provided in one plane, and the secondary windings are in the other plane which opposes closely the one plane.
Recently, video taperecorders, especially, for home use, have become much more compact. However, the relatively larger diameter of magnetic head drums was a bar to that trend. Such a larger diameter of the drums results partially from the fact that in the prior art head drums the coil windings of a rotary transformer were disposed in planes extending perpendicularly to the central axis of the drum cylinders. This becomes more significant in a rotary drum assembly of the type in which a number of, for example, four video heads are provided on a single rotary head drum. With such a type of drum assembly, the provision of an increased number of video heads gives rise to a smaller diameter of the drum mounted with a correspondingly increased number of windings of the rotary transformer.
In the prior art, there is known the type of a rotary head assembly in which a mechanical contact of a surface of magnetic tape with the cylindrical surface of the head drum is minimized by the effect of an "air film" due to the air flow which is produced between opposed surfaces, so as to smooth out the running of the tape with less frictional force. See Japanese Patent Laid-Open Publication Nos. 24506/1977 and 24507/1977, for example. In order to establish such an air flow, there are rotary head assemblies which are provided with a fan or blower, and ones which have a rotary drum with a number of grooves cut generally radially on its surface opposing the stationary drum. Those features result in preventing the assemblies from being miniaturized, and may cause dust and oil to be trapped in those grooves so as to decrease the performance and reliability of the machines. Those difficulties were more critical to video taperecorders for home use, in which further miniaturization and ease of maintenance are required.
In the case of drum assemblies provided with more, for example, four, video heads on a rotary cylinder than conventional ones with two video heads, the cylindrical drum is smaller in diameter and rotates at a higher speed, and the tape contact angle is larger, which is the central angle of a sector of the head drum formed by a portion of the peripheral surface that is in contact with the tape. For example, the contact angle may be more than 270 degrees in the case of a four-head drum assembly. Such a larger contact angle may often disturb the tape from running smoothly to cause visually irritatable jitters to appear in pictures on display. Therefore, simple and compact structure as well as smooth tape running are desired in the field of video taperecorders.